Friction lining and method for manufacturing a friction lining

ABSTRACT

In the case of a friction lining, intended in particular for brake systems and comprising a friction element consisting of asbestos-free friction lining material and an abrasive element consisting of abrasive material with a thermosetting binder on the basis of natural or synthetic resin, it is provided that an abrasive element is incorporated in the friction element which, as wear of the friction lining advances, enables the frictional properties of the surface which presses against the lining to be regenerated at intervals.

BACKGROUND OF THE INVENTION

From DE 21 33 455 A1 and DE 23 62 190 A1, friction linings are known onthe free surface of which an abrasive layer is provided which serves forevening out surface variations, particularly flute formations on thecounterpart of the friction lining, by abrasion.

This flute formation is said to be evoked by insufficient possibilitiesfor removing chips in case of surface contact of the frictionalpartners. Known abrasive layers consist of abrasive particles, e.g.carborundum, Al₂ O₃, pounce and the like, which are bound with one orseveral binders, modified phenolic resins or the derivatives thereof,such as cresol resin and the like.

The binding agents on the basis of natural or synthetic resins havethermo-setting properties and a temperature stability corresponding tothat of the frictional material

From DE-A-23 62 190, it is known to give a wave-shaped configuration tothe abrasive layer on the surface of the friction lining in order toprovide for a reliable removal of chips in any operational state of thebrake. The layer thickness of the abrasive layer amounts toapproximately 0.3 to 0.6 mm.

So far, the known abrasive layers have been used in connection withbrake pads containing asbestos.

Due to the legally regulated introduction of asbestosfree brake pads,new problems arise in practice during the operation of brakes equippedin such a manner.

Checks of such braking systems have shown that the wear behaviour at alow temperature is much more unfavourable than in case of brakes withasbestos-containing pads, i.e. the wear of the brake disk is higher atlow working temperatures of the brake. This is particularlydisadvantageous with vehicles in short-distance operation, wherein thebrake arrangements do not reach elevated working temperatures, but alsowith vehicles driven over a long distance, wherein the brake arrangementmay cool down completely between two braking processes.

FIG. 1 shows the quantitative wear behaviour V of the brake disk independence on the temperature [C°] for asbestos-containing (a) andasbestos-free (b) brake pads in comparison. The different wear behaviourmainly depends on the working temperature of the brake arrangement.

The latter promotes the formation of nonuniform wear, namely differencesin thickness, at the brake disk. These differences in thickness resultin the so-called brake rubbing, i.e. in strong braking force variationsduring the braking process. This leads to vibrations of low frequencywhich may be transferred to the components of the entire vehicle andthus impair driving security and the service life of the brakearrangement.

According to present knowledge, these differences in thickness areproduced by periodical contact of the pad with the rotating disk in thenon-braked state. These may be caused, e.g., by tolerances of the brakearrangement with respect to measurements, withdrawal moments of thewheel brake cylinders or of axis components,

From DE 28 21 323 A1, a brake friction block is known wherein anintermediate layer being embedded in the friction lining is provided,which serves as heat barrier.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a friction lining withabrasive elements which also permits, during the advancing wear of thefriction lining, a regeneration of the friction-technical counterpart ofthe friction lining in the meantime.

To arrange abrasive elements in layers has the advantage that thefriction lining can function as friction element and that the abrasiveelement is not used until after certain states of wear of the frictionlining have occurred so that a regeneration of the friction-technicalcounterpart of the friction lining is regularly effected afterpredetermined laid-up times.

In case of such a configuration of the friction lining, however, it isnecessary that the coefficient of friction of the abrasive elementmatches the coefficient of friction of the friction element in order toavoid friction coefficient differences.

A further solution according to the invention is to provide an abrasiveelement extending transversely to the direction of movement of thefriction-technical counterpart of the friction element in a partialportion of the friction element over the entire width of the frictionelement and, starting from the surface of the friction element, into thedepth, and/or with a friction element consisting of a mixture offriction lining material and abrasive material, which, compactedtogether, form a combined uniform friction and abrasive layer.

Due to the fact that the friction element extends transversely to thedirection of movement of the friction-technical counterpart of thefriction element in a partial portion of the friction element over theentire width of the friction element and, starting from the surface ofthe friction element, into the depth, continuous abrasing of thefriction partner, e.g. a brake disk, is possible, so that the formationof unevenness due to the surface contact of the friction partners isavoided. Such a preferably strip-shaped arrangement of the abrasiveelement within the friction element also has the advantage to have auniform influence on the coefficient of friction of the frictionlinings, so that the abrasive element need not necessarily have the samecoefficient of friction as the friction element.

Another solution, according to the invention, is to fibre-reinforce theabrasive element with a percentage by weight/volume of about 1 to 30%,preferably 5 to 20%.

All natural mineral, synthetic mineral and/or organic fibres, such asbasalt, aramide, carbon, glass or ceramic fibres can be used as fibrereinforcement.

In one embodiment, the fibre-reinforced abrasive element contains amixture of aramide, glass and/or carbon fibres, an adaptation to thecoefficient of friction of the friction element being effected via themixing ratio of the fibres. In this case, the effect of the fibres isutilized, aramide fibres, for example, generating a soft abrasive effectand glass fibres a hard abrasive effect.

According to the method of the invention, it is provided to separatelymanufacture layer-shaped abrasive elements, for example by extrusion,pressing or punching, and to subsequently compact these layer-shapedabrasive elements together with already prepressed friction elementlayers or with pulverized friction material.

Referring to the drawings, embodiments of the invention will bedescribed in detail.

BRIEF DESCRIPTION OF THE DRAWINGS

In the Figures:

FIG. 1 shows a comparison of the wear behaviour of brake disks independence on the temperature of the brake disk;

FIG. 2 shows a first embodiment of a friction lining comprisingintegrated abrasive element layers;

FIG. 3 shows a second embodiment with a strip-shaped abrasive elementextending axially over the entire width of the friction lining;

FIG. 4 shows a front view of the embodiment according to FIG. 3;

FIG. 5 shows a brake block including a friction lining consisting of amixture of friction lining material and abrasive material, and

FIG. 6 shows a brake block with a combination of different abrasiveelements.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 shows layer-shaped abrasive element layers 6 integrated in afriction lining 1 consisting of several friction element layers 4.

The different layers 4,6 can be readily manufactured. There is thepossibility to lay them, in the form of a sheet, into the compressionmould or to manufacture the layers 4,6 according to the known method bydumping and pressing the layer materials. With respect to the dumpingand pressing method, the sheet has the advantage that the thickness ofthe layers can be arranged in the friction lining 1 in a preciselydefined manner, always having a constant thickness. The advantage ofsuch a brake block or friction lining is that the friction-technicalcounterpart, in this case a brake disk, is regularly regenerated,corresponding to accurately defined states of wear, namely after thewear of a certain friction layer 4, by means of the abrasive layer 6.

In this embodiment, it is essential that the coefficient of friction ofthe abrasive element layer exactly matches the coefficient of frictionof the friction element layer, so that no friction coefficientdifferences arise in case of different states of wear of the respectivebrake blocks.

FIG. 3 and FIG. 4 show another embodiment wherein the abrasive elementaxially extends from the surface of the friction lining 1 into the depthand radially over the entire width of the friction lining 1, andactually orthogonally to the direction of movement of the counterfriction surface, which is the brake disk in this embodiment. Theabrasive element extends to just before the lining support plate 2 butdoes not contact it. Such a friction lining guarantees a continuousabrasive process.

FIG. 5 shows another embodiment, wherein the abrasive layer material isconditioned as granule and mixed, in defined quantity, with the frictionlining material and compacted to form a uniform mass together therewith.Such a friction lining has the advantage that the abrasive function,similar to the embodiment of FIG. 3, is continuously effective duringthe entire service life of the brake pad and thus maintains the counterfriction surface, i.e. the brake disk, in an optimum state. The abrasiveeffect can be easily adjusted by means of the recipe, i.e. individualideal friction conditions can be established for the differentrequirements made on the brake arrangement and the corresponding brakepad.

The reinforcement of the abrasive material with aramide fibres generatesa rather soft abrasive effect and a reinforcement with glass fibres aneffect to the contrary.

The mixture of various fibres, e.g., aramide fibres, glass fibres, andcarbon fibres, and the proportional ratio with respect to each otherpermit to predetermine different abrasive effects and to optimumly adaptto the coefficient of friction of the friction lining.

FIG. 6 shows an embodiment wherein the abrasive element 6 is partlyarranged as an intermediate layer between successive friction elementlayers, partly extends, starting from the surface of the frictionelement, in the form of a strip over the entire width orthogonally tothe direction of movement of the friction-technical counterpart of thefriction element, e.g. a brake disk, into the depth of the frictionelement, and/or, by being added to the friction lining material, ispartly compacted in combination therewith to form a friction/abrasivelayer.

The abrasive element in the form of an intermediate layer can also becombined only with the abrasive additive to the friction liningmaterial.

What is claimed is:
 1. A friction lining for refurbishing a frictionalsurface of a braking means comprising a layer shaped friction elementcomprising an asbestos-free friction lining material and a layer shapedabrasive element comprising abrasive material with a thermo-settingbinding agent of natural or synthetic resin, characterized in that saidabrasive element (6) is arranged, as an intermediate layer, betweensuccessive friction element layers (4) whereby upon the wearing away ofa friction layer element (4), a successive abrasive element (6) isexposed for abrading away and smoothing said frictional surface therebymaintaining said surface in an optimum state.
 2. The friction liningaccording to claim 1, characterized in that an additional abrasiveelement (6) extends, in the form of a strip, starting from the surfaceof said friction element (1), over the entire width orthogonally to thedirection of movement of an associated brake disk into the depth of thefriction element (1).
 3. The friction lining according to claim 1,characterized in that said abrasive element (6) is fibre-reinforced witha percentage by weight/volume of about 1 to 30%.
 4. The friction liningaccording to claim 3, characterized in that said fibre-reinforcedabrasive element (6) contains aramide fibres. of about 1 to 30%,preferably 5 to 20%.
 5. The friction lining according to claim 3,characterized in that said fibre-reinforced abrasive element (6)contains aramide fibres.
 6. The friction lining according to claim 3,characterized in that said fibre-reinforced abrasive element (6)contains carbon fibres.
 7. The friction lining according to claim 3,characterized in that said fibre-reinforced abrasive element (6)contains a mixture of aramide fibres, basalt fibres, natural mineralfibres, synthetic mineral fibres, glass fibres, ceramic fibres or carbonfibres, and in that the coefficient of friction of the friction element(4) is achieved by the ratio of the admixed fibres.
 8. The frictionlining according to claim 1 characterized in that said abrasive element(6) is fibre-reinforced with a percentage by weight/volume of about 5 to20%.
 9. The friction lining according to claim 1 wherein all layersexhibit substantially the said coefficient of friction.
 10. A method ofmanufacturing friction linings by compacting an asbestos-free frictionlining material to form friction element layers, characterized byseparately manufacturing a layer-shaped abrasive element by extruding,pressing or punching and by subsequently compacting the layer-shapedabrasive element, as an intermediate layer, together with severalfriction element layers whereby in use the wearing away of a frictionelement layer exposes a successive abrasive element for abrading awayand smoothing an associated frictional surface thereby maintaining saidsurface in an optimum state.
 11. The friction lining manufacturingmethod according to claim 8 wherein all layers exhibit substantially thesame coefficient of friction.